Characters

Question 1

What is a character

Answer 1

A character is a (presumed) heritable feature that varies within a study group

Question 2

What are some examples of characters

Answer 2

• morphology
• molecular sequence data of proteins or DNA

Question 3

What is total evidence

Answer 3

Analyses that simultaneously use all kinds of characters (these use all the available information)

Question 4

What is reciprocal illumination

Answer 4

mapping characters in an independently derived phylogeny which can help to determine whether they are homologous

Question 5

What is a character state

Answer 5

A state is one of the alternate conditions of a variable feature (character)

Question 6

Describe this in the language of morphological character statements used in formal taxonomic descriptions

–> Eyebrow hair colour: black (format is always character: state)

Answer 6

Eyebrow hair = Locator (L)
Color = variable (V)
Black - Variable condition 0
Blonde - variable condition 1
(these are the character states)

Question 7

What is a binary character

Answer 7

a special case of a character with two states

Question 8

what is a multi state character

Answer 8

when there are 3 or more states

Question 9

When is a taxon considered polymorphic for a character

Answer 9

when two or more states are known in a single terminal taxon

Question 10

When can a character be informative

Answer 10

• if it varies within the ingroup
• and if its alternative states EACH occur in two or more taxa within the total group (ingroup and outgroup)
• a binary character can only be informative if there are at least 4 taxa in the study, because each state must occur at least twice

Question 11

What does ordering of states mean

Answer 11

ordering specifies the number of evolutionary steps separating pairs of states - this is only relevant for multi-state characters

Question 12

What is an unordered state

Answer 12

any state can change to any other state by one evolutionary step. This is the most common assumption

Question 13

How do you decide whether to order or not order a state

Answer 13

do not order a character if states can change from one to another without passing through an intermediate state

Question 14

What does irreversibility in a phylogenetic tree do

Answer 14

it forces convergence rather than reversal when more than one step is needed on a particular tree

Question 15

What are the 2 types of mutational changes among the four states in DNA data

Answer 15

1. transitions = changes between 2 purines or between 2 pyrimidines (this is frequent)
2. transversions = changes between a purine and a pyrimidine (this is infrequent)

Question 16

Describe the weighting of characters

Answer 16

• weighting specifies the “cost” in number of steps for a change of state. It estimates how unlikely an event is. Assuming a high weight makes a character more influential in the final outcome of the analysis = a more valuable source of phylogenetic information because you think it is less likely to evolve independently more than once

Question 17

Describe the coding of characters

Answer 17

The process of putting character information in a format used for phylogenetic analysis (analysis usually performed by computer algorithms) - usually discrete states are used

Question 18

If you think that transversion are a lot less likely (4X) than transitions then how many steps would it take to go from G–>A and from A–>C

Answer 18

G–>A = 1 step (this is a transition between 2 purines)

A–>C = 4 steps (this is a transversion which is 4 times less likely so therefore it would take 4 steps to get this occurrance)